The intermediate nucleus tractus solitarious (NTS) is a critical neural component in the control of upper airway reflexes such as swallowing and apnea. Anatomical, physiological and behavioral studies over the last several years have provided evidence that chemical information from taste buds in the upper airway play an important part in the initiation of swallowing and apnea produced by introduction of fluids into the upper airway. Afferents from upper airway receptors, including taste buds, project via the SLN on to cells in the intermediate NTS. Specifically, recent studies have demonstrated that a compact cellular NTS region located ventromedial to the solitary tract receives the majority of chemical and mechanical information from upper airway receptors. Other studies have shown that injections of putative neurotransmitters into this NTS region influence upper airway reflexes such as swallowing. Presently, little is known about the neurobiology of NTS neurons receiving upper airway sensory inputs or abut the neural substrate in the intermediate NTS which underlies upper airway reflex behaviors. Proposed experiments will examine in detail the anatomical, neurochemical and functional characteristics of NTS neurons. Neuroanatomical studies will be used to determine the morphology and neurochemical composition of neurons in reflexogenic NTS regions responsive to stimulation of the upper airway. An in vitro brain slice preparation will be used to investigate intrinsic response characteristics of neurons in NTS areas involved in sensory-evoked reflexes of the upper airway. Intracellular recordings and reconstruction of dye-filled neurons will be used to determine structure-function relationships. Transneuronal tract-tracing techniques will be used to determine the connections of intermediate NTS neurons receiving upper airway afferent inputs. These experiments will provide basic information about neurons in a region of the NTS that receives afferent input from upper airway sensory receptors and is involved in the regulation of upper airway reflexes such as swallowing. Because the neuro biology of this NTS region is not yet characterized in depth, these investigations will provide new data. Such studies can provide evidence for important roles of the taste system in processes not directly related to recognition and ingestion of food. Furthermore, this information will contribute to our understanding of the neural regulation of swallowing, apnea and other reflexes of the upper airway.